All you need to use it is your iPhone/iPod Touch and the needle or hook you want to size.

How to find a needle size

Locate the white stripe that is approximately the width of your needle. You may need to scroll up or down to do this. (Use your finger to scroll the needle sizes up or down.)

It's easiest to start with a stripe that is too large and work your way up the screen.

Lay the needle directly over the white stripe until you find one where the needle completely hides all of the white and you can see the red stripes glowing above and below the needle.

Too big! Try the next one up.

Still too big! Try the next one up.

Just right! I can see red lines glowing above AND below the needle. This must be a 5.0mm US8 needle.

Let's just move up one to see what it looks like.

I see the red glowing line above the needle, but not below it.

This one is too small.

Close up of the glowing lines indicating a match.

Note: Different companies size their needles and hooks a little differently, including designating different mm sizes for US sizes. iKnit Needle Sizer lets you discover the true size of any needle regardless of company variation. Always choose needles that give you the gauge you need for a project, which may be a different size than suggested in the project directions. To be sure you have the right gauge, try our app, KnitGauge, which lets you measure your gauge with amazing precision and ease.

Also note: When measuring the smallest sizes (1.75 mm - 3.0 mm), be sure to choose the widest stripe where your needle covers all the white yet leaves all the red showing top and bottom. If you choose one size too small, you may still see red on both sides, but you are covering up a portion of a red line.

I want to acknowledge my team of advisors, testers, and editors, Mary Danca, Cat Bordhi & Sandi Golden. I truly appreciate your never ending enthusiasm, ideas and support. The iKnit apps would not be the same without your help. Thank you!

Many thanks to Cat Bordhi for the idea of using white stripes to measure the needles. (It worked!) You can see more of Cat's books, knitting patterns and much much more at www.catbordhi.com.

Thanks also to Kristin Omdahl for supplying the most common crochet hook US sizes by mm. She has a great web site at www.StyledByKristin.com.